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/// \file B1/include/PrimaryGeneratorAction.hh
/// \brief Definition of the B1::PrimaryGeneratorAction class

/* 在真实世界中, 确定粒子源需要两个信息: 粒子源的物理信息与几何信息. 
在Geant4中, 也可以把确定粒子源分为确定粒子源的 物理信息 与 几何信息 这两个步骤, 
这些信息一般都被写在文件"PrimaryGeneratorAction.hh/.cc"中, 
这里的英文名称直译是"基本产生/初级粒子", 但实际上"基本"指的就是在程序中的粒子源产生粒子, 
因为产生粒子之后才能模拟粒子与材料的相互作用. 
*/

#ifndef B1PrimaryGeneratorAction_h
#    define B1PrimaryGeneratorAction_h 1
#    include "G4VUserPrimaryGeneratorAction.hh"  //一般用户自定义的PrimaryGeneratorAction类继承于此

class G4ParticleGun;  //使用G4ParticleGun作为粒子源
class G4Event;        //成员函数中的参数中含有G4Event类，故提前声明
class G4Box;

namespace B1
{

    /// The primary generator action class with particle gun.
    ///
    /// The default kinematic is a 6 MeV gamma, randomly distribued
    /// in front of the phantom across 80% of the (X,Y) phantom size.
    class PrimaryGeneratorAction : public G4VUserPrimaryGeneratorAction
    {
    public:
        PrimaryGeneratorAction();
        ~PrimaryGeneratorAction() override;

        /// method from the base class; 一般在此函数中指定粒子源的相关信息
        ///该成员函数将在每个event开始时被调用一次
        void GeneratePrimaries(G4Event*) override;

        /// method to access particle gun; 用于访问私有变量 fParticleGun
        const G4ParticleGun* GetParticleGun() const { return fParticleGun; }

    private:
        /// G4ParticleGun的指针fParticleGun
        G4ParticleGun* fParticleGun = nullptr;  // pointer a to G4 gun class; RAII
        G4Box* fEnvelopeBox = nullptr;
    };

}  // namespace B1

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#endif
